1. Black body radiation
Why do objects have colour? Would this effect the light they emit if they were hot? What colour would a cold star be?

2. A reminder before we go on….

3. Apparent and Absolute Magnitude
This means that a star that is one magnitude (absolute) brighter than another star is actually 2.51 times brighter than it
Remember brighter objects have lower magnitudes
Calculating the absolute magnitude M of a star from it's apparent magnitude m and distance D (in parsecs) is done using this formula:
Note that there are various ways of writing this formula so you may get a different form in the exam

4. Black body radiation curve
By analysing the curve of the output of a star against wavelength you can estimate the temperature of the star's surface.

5. Wein's Displacement Law
The peak of a blackbody curve can be calculated from the Temperature of an object using Wein's displacement law (and vice versa from analysis of the spectrum of light from a star):
Use the formula above and the chart (in nm) to estimate the temperature of the following stars:
Betelgeuse - Red
Rigel - Blue
Sun - Yellow

6. Oh Be A Fine Girl Kiss Me Spectral Classes
Once you know the surface temperature of a star then you can assign it to a Spectral Class
Oh Be A Fine Girl Kiss Me
Spectral Class
Surface Temperature /103 K
Colour O
25 – 50
Blue B
11 – 25 A
7.5 – 11
Blue / White F
6.0 – 7.5
White G
5.0 – 6.0
Yellow / White K
3.5 – 5.0
Orange M
< 3.5
Red

7. Light with a slightly shorter wavelength than 400nm
Ultraviolet
Light with a slightly longer wavelength than 700nm
Infrared
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8. Spectral Type vs Emission Spectra
A star emits light because it is hot however there are absorption lines in the spectrum due to the presence of molecules, atoms and ions in the photosphere and the corona. The temperature of the star will effect which chemicals will be present.

9. Fraunhofer Lines

10. Line Spectra
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11. Atomic Spectra
Continuous spectrum
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12. Atomic Spectra Continuous spectrum Slide No. 01869 336410
"Bohr-atom-PAR" by JabberWok at the English language Wikipedia. Licensed under CC BY-SA 3.0 via Wikimedia Commons -
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13. Balmer Series

19. Power and Flux
Stefan's law links Temperature of a star to it's Luminosity (in Watts)
Flux is the power per unit area at a position d distance from the star:
This is sometimes called the power of the star and the L is replaced with a P

20. Flux from the Sun at different planets
Given that the power of the sun is 3.839x1026 Watts, what is the flux at each of the planets below?
What assumptions have you made in this calculation?
You have assumed that the atmospheres do not absorb any radiation

21. Summary
Stars are black body absorbers meaning that they emit a near perfect spectrum of radiation
The temperature of a star can be calculated from the peak wavelength of the emission
The temperature then places the star into a classification
The spectrum will also contain absorption lines which will help to confirm the temperature of the star
Cooler stars contains molecules, warmer ones contain metal ions, very hot stars contain helium ions